History of advertising: No 177: Robert Townsend's all-staff memo

But Townsend knew something dramatic was needed if Avis was to close the gap on Hertz, its biggest competitor and the US market leader, whose adspend was five times bigger.

What’s more, he had faith in Bill Bernbach, the creative spark plug at the Avis agency, Doyle Dane Bernbach.

"If you promise to run whatever we recommend," Bernbach told Townsend, "every creative in my shop will want to work on your account."

To minimise risk to the maximum, Townsend wrote a memo, framed copies of which went up in all offices at Avis and DDB.

"Avis will never know as much about advertising as DDB and DDB will never know as much about the rent-a-car business as Avis," Townsend wrote.

He went on to promise that Avis would not approve, disapprove or try to improve ads and insisted that DDB submit only those as it truly recommended. "They will not ‘see what Avis thinks of that one’."

The brief was tough. The Avis fleet was not newer than its rival’s, it did not have more rental locations and its rates weren’t cheaper.

It was Paula Green, a DDB copywriter, who cracked it with a slogan that went completely against the prevailing Madison Avenue philosophy that ads must never acknowledge a brand weakness. Her line, "We try harder", was the catalyst for one of the most famous campaigns in advertising history.

Within a year, Avis had turned a $3.2m loss into a $1.2m profit – its first in 13 years – as its market share increased significantly.

Things you need to know

Hertz initially ignored the Avis attack but, with its market leadership under threat, responded with a 1966 ad, which read: "For years Avis has been telling you Hertz is No 1. Now we’re going to tell you why."

Green once likened her line to her own challenges as a female creative: "‘We try harder’ is somewhat the story of my life."

Avis, which never succeeded in catching Hertz, dropped the "We try harder" line in 2012 in favour of a Leo Burnett campaign targeting business travellers under the theme "It’s your space".